This application claims the priority of German application No. 198 08 167.7, filed Feb. 27, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and a motor control apparatus for correcting a computer-established torque in the drive train of a motor vehicle.
German patent document DE 39 14 167 A1 discloses a safety system in a motor vehicle for ensuring that the throttle valve of the internal combustion engine will return to the closed position when the accelerator pedal is not operated, even in the event of failure of the throttle valve control system. The gas pedal position and the torque at the output of the transmission are detected by sensors; the torque is compared with a predetermined minimum value and an error signal is produced if the actual torque exceeds the minimum value. The error signal acts upon a system for interrupting the operation of the internal combustion engine.
This system only takes into account the failure of the throttle valve control system, and thus no other additional facilities for control and steering are possible (especially facilities for affecting road stability). Another disadvantage is due to the use of the torque sensor, whose use in large series production has yet to be satisfactorily solved.
The invention provides an improved method and control apparatus which, on the basis of predetermined signals representing the state of the motor and transmission, determine the torque by computer and perform a computerized adjustment using known torque levels at certain known points of operation. In this method, the use of a torque sensor can be dispensed with; determination of the torque is performed exclusively by computer, on the basis of factors which are easy to detect via sensors (for example, by sensing engine speed). By adjusting the difference between computed and known torque levels, an attempt is made to reduce systematic errors which affect torque computations.
German patent document DE 43 04 779 A1 discloses an apparatus for controlling the output torque of a drive unit of a vehicle. For this purpose, power parameters of the drive unit (i.e., the motor torque losses and the torque required by auxiliary units) are computed and subjected to correction by comparing actual values obtained from measuring systems to the theoretical values determined in the control apparatus. The determination of the theoretical torque, however, again requires the use of a torque sensor.
German patent document DE 195 27 130 A1 discloses a power transmission control apparatus which has a microcomputer for computing and estimating the values of the torque at the input of a torque converter for an automatic transmission, and includes the values of the transmission ratio of the automatic transmission. For this purpose, certain characteristics of the motor and the torque converter are determined experimentally and stored in performance characteristics. Using equations stored in the microcomputer which represent these characteristics and the values sought for the torque and the transmission ratio, it is possible to obtain estimates of the desired values.
In this case, the strong influence of the power absorbed by auxiliary equipment of the vehicle (the air conditioner, for example) upon the reference value of the torque is problematic. As a result, an accurate separation of the signals of the known torque into a percentage for association with the motor and a percentage for association with the auxiliary equipment is not possible. Depending on the operating state which is used as the basis for determining the reference value of the torque, the torque will be composed of different percentages for the motor and the auxiliary equipment. The value for the correction of the computed torque thus fluctuates according to the operating state of the motor and the active auxiliary equipment.
In view of the foregoing, it is an object of the invention to provide a method and motor control apparatus for mathematically determining the torque in the drive train of a motor vehicle as accurately as possible.
This and other objects and advantages are achieved by the method and motor control apparatus according to the invention, in which a recognition signal for distinguishing between automatic and manual transmissions is produced, and motor and transmission operating states (selected in accord with the recognition signal), in which the actual torque applied to the crankshaft is equal to zero, are established. Furthermore, when these motor and transmission operating states are reached, the mathematically determined torque associated with the operating states is compared with the actual torque, and the difference between the mathematically determined torque and the actual torque is used as a control factor for the correction of additional computed torques.
The method and motor control apparatus according to the invention, permits a reduction of the systematic error in the computation of the torque. Moreover, the method and motor control apparatus can be used in both automatic transmissions and manual transmissions. Automatic transmissions and manual transmissions are distinguishable by a recognition signal. As a result, separate construction of the motor control apparatus for each type of transmission is unnecessary.
The recognition signal is used to select the parameters and levels for the description of the operating states of the motor and transmission. Different states are taken into account according to the type of transmission for which an adjustment between the calculated torque and the actual torque must be satisfied. The motor and transmission operating states are selected such that there is no load on the crankshaft; that is, so that the actual torque applied at the crankshaft is equal to zero. The torque which is computed for this state is then obtained and compared with the (actual) zero torque. Any departure of the computed torque from zero is used as the control factor for the correction of additional, mathematically determined torques. The correction of the torque is performed preferably with the accessories turned off, in order to avoid falsification of the actual zero torque obtained and to be able to determine the difference in the computed torque.
In an embodiment of the process, the computed torque is composed of two components, an effective torque and a residual torque to allow for torque losses. These are especially composed of the addition of torque losses inherent in the motor and a torque adaptation value for improving the accuracy of the computed torque. The control factor (multiplied by a weighting factor in some cases) can be added to the torque adaptation value, if the computed torque is not equal to zero (in the state in question). In this manner, a shift of the torque adaptation value is obtained, and consequently a correction for all computed torques for all motor and transmission states is achieved. As soon as the conditions are restored for an actual torque equal to zero, a new control factor can be formed and the torque adaptation value can again be modified accordingly.
The conditions for an actual torque equal to zero differ according to the type of transmission. In the case of a manual transmission, the transmission is advantageously idling, the vehicle speed is zero, and the motor must be at its working temperature. These conditions must be satisfied in order to exclude non-static and dynamic influences.
In the case of an automatic transmission, the operating state of the converter is preferably used in determining the conditions. The actual torque is zero, provided that the crankshaft speed corresponds approximately to the speed of the driven wheels, so that the two rotors of the converter have approximately the same speed. In addition, an allowance can be made for the vehicle""s speed and the motor temperature.
The motor control apparatus according to the invention, comprises various intercommunicating modules. In a first module, a recognition signal is produced in order to distinguish between automatic and manual transmissions. In a second module, a status signal is produced which indicates whether the motor and transmission operating states at which the actual torque applied to the crankshaft is equal to zero have been reached. In a third module, a torque adaptation value is formed from the difference between the computed torque and the actual torque; the third module can be activated by the status signal from the second module.
This embodiment has the advantage that all conditions which must be satisfied in order for the actual torque to be equal to zero can be determined and checked in advance before the computation of the torque adaptation value is performed. Furthermore, both automatic and manual transmissions can be covered by only one motor control apparatus.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.